The goal of this R21 exploratory proposal is to determine whether the V-1 isolate, termed Vilyuisk human encephalitis virus (VHEV), which may represent a separate clade of theilovirus, is the causative agent of Vilyuisk encephalomyelitis (VE). Although the viral cause of VE remains unknown compelling evidence links VHEV to VE. VE has spread 400 km from the area of endemicity along the middle reaches of the Vilyui River to a new more populous geographic area in the Lena-Aldan river valleys where Yakutsk, the capital of the Sahka Republic in Siberia (Russia), is located. Globalization due to increased freedom of air travel could result in further spread of VE to other regions of the world. Recent identification of theiloviruses designated Saffold viruses (SafV) in children with respiratory and diarrheal diseases from separate geographic locations in North America and four other continents indicate that theiloviruses are global in distribution and commonly infect children and possibly adults. The emergence of theiloviruses is the catalyst for our renewed interest in the cause of VE since it is creditable that theiloviruses cause human central nervous system (CNS) diseases. In fact, the PI has just learned of SafV isolations from cases of encephalitis in children in Europe. Therefore, it is intriguing to speculate theiloviruses represent an emerging group of human viruses that cause central nervous system CNS infections, including VE (hypothesis). Two specific aims are proposed: (1) To investigate a link between VHEV and the clinical disease of VE, we will determine serum titers and serum:CSF ratios of ELISA and neutralizing antibodies to VHEV in VE cases and controls, VE cerebrospinal fluid (CSF) oligoclonal band (OCB) reactivity to VHEV, and whether a 320- bp Cardiovirus amplicon that includes the highly variable VP2 puff (EF) structures can be amplified from total RNA extracted from VE CSF. (2) In the event that VHEV cannot be linked to VE, reverse transcribed cDNA from total RNA extracted from VE CSF will be hybridized to oligonucleotide viral microarrays (GreenChipsPm) and also used for high-throughput sequencing to detect foreign (non-human) sequences of a specific vertebrate virus family by subtraction of the human transcriptisome. PUBLIC HEALTH RELEVANCE: This is an exploratory proposal to determine the viral cause of a chronic central nervous system disease that occurs in the Sahka Republic in far northeastern Russia (Siberia). This disease, Vilyuisk encephalomyelitis, has some similarities to multiple sclerosis and appears to be caused by a human Theilovirus. The murine counterpart, Theiler's murine encephalomyelitis virus, provides a highly relevant experimental animal model for multiple sclerosis.